1. Field of the Invention
The present invention relates generally to the field of cancer therapy. More particularly, it concerns the use of methoxyestradiol to stimulate p53 expression in tumor cells, thereby inducing programmed cell death.
2. Description of Related Art
Normal tissue homeostasis is achieved by an intricate balance between the rate of cell proliferation and the rate of cell death. Disruption of this balance is thought to be a major deleterious event in the development of cancer. The inhibition of apoptosis (programmed cell death) has been linked to this disruptive event. The effects of such defects are catastrophic, causing over half a million deaths per annum in the United States alone.
The p53 gene is well recognized as a tumor suppressor gene (Montenarh, 1992). There is now considerable evidence linking mutations of p53 in the oncogenesis of many human cancers. There are numerous reports demonstrating that the growth of, for example, colon, glioblastoma, breast cancer, osteosarcoma and lung tumor cells can be suppressed by the expression of wild-type p53.
The introduction of wild-type p53 in a wide variety of p53-mutated cells, using viral delivery methods, has resulted in the expression of the wild-type p53 transgene and a suppression of the malignant phenotype. These observations demonstrate that a high level of expression of wild-type p53 is a desirable course for the treatment of oncogenic malignancy.
As the half-life of p53 is very short, ranging between 15 and 20 minutes, it has proved difficult to increase the expression of exogenous p53 using conventional transfection strategies. The microcellular environment of these cells is such that overexpression of wild-type p53 protein, when achieved, is counteracted by rapid degradation. Hence, delivery of wild-type p53 into cancer cells containing wild-type p53 using conventional viral vectors as a way of reducing tumor growth is at best inefficient. A significant percentage of the cancers retain a wild-type p53 gene, but increasing the expression of these genes likely will suffer from the same limitation.
Therefore, there is a clear need for an approach to sustained induction or increase in wild-type p53 expression in cancer cells to mediate apoptosis in such cancer cells.
It is a goal of the present invention to provide methods for increasing the level of p53 in a target cell. Similarly, it is a goal of the present invention to provide methods for inducing apoptosis in a cell expressing a functional p53. It also is a goal of the present invention to provide improved methods for the treatment of cancers comprising administration of a p53 gene in conjunction with an agent that increase the level of p53 in cells.
In accordance with the present invention, there is provided a method for increasing the level of p53 in a cell having a functional p53 therein, comprising the step of contacting said cell with an amount of 2-methoxyestradiol sufficient to increase the level of p53 in said cell. The p53 may be an endogenous or exogenous protein. The cell may be an endothelial cell or a tumor cell, for example, a lung tumor cell such as a non-small cell lung carcinoma cell.
In another embodiment, there is provided a method for inducing apoptosis in a cell having a transcriptionally active p53 gene therein comprising the step of contacting said cell with an amount of 2-methoxyestradiol sufficient to induce apoptosis in said cell. Again, the p53 gene may be an endogenous or exogenous gene.
In still yet another embodiment, there is provided a method for treating cancer in a patient comprising the steps of (a) determining the p53 status of a tumor cell in said patient; and (b) contacting said tumor cell with an amount of 2-methoxyestradiol sufficient to induce apoptosis in said cell. Where the p53 status of said tumor cell is that it contains a functional p53, further provision of p53 is unnecessary. Where the p53 status of said tumor cell is that it lacks a functional p53 protein, the method further comprises the transfer of a wild-type p53 gene into said tumor cell.
In a particular embodiment, transfer of a p53 gene comprises contacting said tumor cell with an adenovirus containing said wild-type p53 gene. The adenovirus may be replication defective, and in particular, may be lacking at least a portion of the E1 region. Administration of the 2-methoxyestradiol is via intravenous or intratumoral administration.
In still yet another embodiment, there are provided kits for the treatment of cancer using 2-methoxyestradiol.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.